Claus Nielsen
- Published in print:
- 2011
- Published Online:
- December 2013
- ISBN:
- 9780199606023
- eISBN:
- 9780191774706
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199606023.003.0055
- Subject:
- Biology, Evolutionary Biology / Genetics, Animal Biology
The Chaetognatha, or arrowworms, is a small phylum consisting of roughly 120 species of marine, mainly holopelagic ‘worms’. Some species, mainly of Spadella and Paraspadella, are benthic. ...
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The Chaetognatha, or arrowworms, is a small phylum consisting of roughly 120 species of marine, mainly holopelagic ‘worms’. Some species, mainly of Spadella and Paraspadella, are benthic. Protosagitta, from the Lower Cambrian (Chengjiang), is undoubtedly a chaetognath. The chaetognaths have an apparently unquestioned monophyly, but their position is not well established. The group has usually been placed in the Deuterostomia based on the fate of the blastopore, but the nervous system and its ontogeny is clearly protostomian. Molecular phylogeny indicates many different positions for the Chaetognatha: ‘between’ Protostomia and Deuterostomia, for example, or as sister group of Lophotrochozoa + Ecdysozoa. On the basis of structure, embryology, and the Hox genes, the chaetognaths are a basal protostomian group. However, there is no unequivocal evidence to support its sister-group relationship with the protostomes, spiralians, or ecdysozoans.Less
The Chaetognatha, or arrowworms, is a small phylum consisting of roughly 120 species of marine, mainly holopelagic ‘worms’. Some species, mainly of Spadella and Paraspadella, are benthic. Protosagitta, from the Lower Cambrian (Chengjiang), is undoubtedly a chaetognath. The chaetognaths have an apparently unquestioned monophyly, but their position is not well established. The group has usually been placed in the Deuterostomia based on the fate of the blastopore, but the nervous system and its ontogeny is clearly protostomian. Molecular phylogeny indicates many different positions for the Chaetognatha: ‘between’ Protostomia and Deuterostomia, for example, or as sister group of Lophotrochozoa + Ecdysozoa. On the basis of structure, embryology, and the Hox genes, the chaetognaths are a basal protostomian group. However, there is no unequivocal evidence to support its sister-group relationship with the protostomes, spiralians, or ecdysozoans.
